Understanding Cache Penetration, Cache Breakdown, and Cache Avalanche

The author recounts a recent interview where the interviewer asked about three cache-related terms: cache penetration, cache breakdown, and cache avalanche.

Cache penetration occurs when queries for non‑existent data repeatedly hit the database because empty results are not cached, leading to unnecessary load. Cache breakdown (or cache stampede) happens when a hot key expires and a surge of concurrent requests all query the database simultaneously, potentially overwhelming it. Cache avalanche refers to many keys sharing the same expiration time, causing a massive wave of database reads when they all expire together.

The author suggests reading two detailed articles for deeper understanding:

1、《缓存一致性，缓存穿透，缓存击穿，缓存雪崩解决方案分析》
https://www.php.cn/redis/492081.html

2、《聊聊Redis热点key存储问题》
https://www.php.cn/redis/492082.html

Familiarizing yourself with such terminology is essential, as it enables you to discuss and solve caching problems effectively in professional settings.